This invention relates to the manufacture of a pneumatic tire and more particularly to the building of a non-spliced tread into a shaped tire carcass preparator to the molding of the tire into a finished shape.
In the manufacture of pneumatic tires there are several methods used in the construction of tires. One uses the so-called single machine station where a highly-skilled tire builder builds the entire carcass from pieces of unvulcanized material. In such manufacture successive plies are wrapped around a rotatable drum having a liner thereon. Beads are placed on the respective ends of the drum during this process. In addition, chafer strips, breakers and other strips of material are wound around the carcass. The last step consists of applying a precut length of tread cushion onto the unvulcanized materials on the drum and rotating the drum one revolution to wrap the tread stock on the drum. The mating portions of the splice of such tread stock can present problems in weight distribution of the stock as where the stock must be stretched to be spliced or where the tread stock is pulled excessively during the wrapping so that the proposed mating ends which are to be spliced overlap each other. In this instance, the operator will peel back part of the length of tread stock and crowd the tread stock so that the ends thereof will meet in a closed butt splice. This results in a variation in the wall thickness of the tread stock circumferentially of the tire. In some instances, sidewalls, chafer strips and other parts of the tire are added after the tread stock is applied. The tire carcass is then shaped and cured. Other methods of manufacture include a two-stage process wherein the tire carcass is built on a tire drum but shaped in a second step machine where the slab of tread stock is applied. Variations in these processes are numerous. The present invention is primarily concerned with the application of the tread to the green tire being built. The present invention is directed to the applying of a relatively thin strip of tread stock helically around the drum in lieu of a single wrap, with the number of revolutions and overlap being determined by the desired contour of the tread stock and sidewalls if such sidewall is also to be included in the contour to be wound. Such helical winding of the stock permits an even, controlled distribution of the stock, wherein the thickness of each layer of built-up stock is uniform circumferentially of the tire. Such winding of the strip material facilitates the escape of air from the windings and eliminates trapped air pockets. The improved strip winding of the present invention permits a greater degree of control on the overlapping of the strips and in the continuous winding of the helical strip.